1. Field of the Invention
This invention relates to a polyacetal resin composition excellent in heat stability and surface processability.
2. Description of the Prior Art
Generally speaking, plastics are quite stable chemically and molded products thereof made by injection molding or the like have a smooth surface, so that it is difficult to decorate the surface thereof by means of printing, coating, deposition or the like or to subject the surface to processing such as adhesion by means of adhesives. Since polyacetal resin is particularly poor in surface activity and there is known no appropriate solvent having an affinity for polyacetal, the surface decoration and adhesion thereof are difficult to carry out in practice and, thus, polyacetal resins are scarcely put to uses requiring such treatments at the present stage. Conversely speaking, since polyacetal resin is excellent in mechanical properties, it is mainly used for mechanical parts or the like in many cases and its surface decoration has not been required hitherto so frequently.
However, the application of plastics has diversified recently and higher class usages are frequently required to simultaneously satisfy plural performances, such as function and appearance or function and adhesion property, of which compatibility has not necessarily been required hitherto. Thus, it is the current trend to require good surface processability even in the application of polyacetal.
Although it is difficult to say that the process for improving surface processability of polyacetal has actively been studied hitherto, we are informed of the fact that the surface processability can be improved to some extent by treating the surface of a molded product with an acidic solution or an oxidant solution. As said acidic solution, p-toluenesulfonic acid, camphorsulfonic acid, phosphoric acid, acid ammonium sulfate and the like have been proposed, while as said oxidant solution a chromic acid-sulfuric acid mixture has been proposed.
The object of the treatment with these solutions is considered to consist in producing a rough surface by chemically etching the surface of a molded product of polyacetal resin and simultaneously forming reactive groups on a part of the polyacetic molecule by the oxidizing action of the solutions. In general, if it is attempted to enhance the effect of a surface treatment by means of such a procedure, problems arise such as deterioration of the parent material, i.e. polyacetal resin, throughout the whole of the body of the molded article, the formation of cracks, etc. On the other hand, if the treatment is carried out utilizing a condition which causes no deterioration of the parent material, the effect of the surface treatment is insufficient and a good surface processing cannot be practiced. For these reasons, there has hitherto been known no molded product of polyacetal resin having a sufficient surface processability for practical use.